This invention relates to hydrotreating of hydrocarbon feedstocks and more particularly to catalytic treatment of hydrocarbon feedstocks to effect removal of nitrogen and sulfur, and to reduce Ramsbottom Carbon Residue (RCR). This invention is especially directed toward the preparation of a catalytic composition having excellent hydrotreating activity for the removal of nitrogen and reduction of Ramsbottom Carbon Residue in heavy hydrocarbon stocks. Examples of such heavy stocks are total crude oil, crude residue, atmospheric and vacuum gas oils, cycle oils and lube oils.
Crude petroleum oil, and heavy hydrocarbon fractions and/or distillates derived from crudes, contain components such as nitrogen, sulfur and metals. These impurities may exist in heteratomic compounds and are often present in relatively large quantities. Such impurities may poison or modify catalysts used in the upgrading of petroleum fractions in reforming or cracking steps. Nitrogen and sulfur are also objectionable because combustion of hydrocarbon fuels containing these impurities releases nitrogen and sulfur oxides. Such byproduct gases are noxious, corrosive and present a serious problem in the field of air pollution.
The removal and/or conversion of these impurities is effectively carried out by catalytic hydrotreating, where a feedstock containing sulfur and nitrogen is contacted with a supported catalyst in the presence of hydrogen. Hydrotreating conditions may include a wide range of temperatures, pressures and space velocities as determined by the design of commercial refineries.
Supported catalysts can be generally characterized as comprising metallic components, supported on a refractory inorganic oxide carrier of synthetic or natural origin and having a medium to high surface area (typically greater than 50 m.sup.2 /g) and a well-developed pore structure. Metallic components having hydrotreating activity may include the metals of Groups VIB and VIII of the Periodic Table. The "Periodic Table" as herein referred to appears in the 62nd Edition of the Handbook of Chemistry and Physics, CRC Press Inc., Boca Raton, Fla. (1981).
Group IVB metal components (for example, titanium) can be incorporated into the catalyst as a promoter to increase the activity of the catalyst. Phosphorous components are commonly incorporated into the catalyst to improve its activity by increasing its acidity; however, the prior art (U.S. Pat. No. 3,840,473) has taught that when the presence of phosphorous is greater than about 0.5% by weight in a titanium-containing catalyst, phosphorous is detrimental to the activity of the catalyst.
Numerous disclosures have been made directed to methods for preparing supported catalyst for hydrotreating. Catalytic metals may be applied to a formed or unformed carrier by several methods known in the art which include co-precipitation of the support with active metals and promoter (also known as the co-gell method), co-mulling the active metals and promoter into a peptized alumina substrate and by various impregnation procedures.
U.S. Pat. No. 3,401,125 discloses co-precipitation of the support with active metals including Group IVB to give an active catalyst similar in hydrodenitrogenation activity to the catalyst of the instant invention; however, this method requires washing steps that are expensive, and the metals, particularly the molybdenum, may be partially washed off the catalyst.
U.S. Pat. No. 4,465,790 discloses a hydrodenitrogenation catalyst which utilizes catalyst supports of alumina-titania prepared by a process starting with co-precipitation of the metals as a hydrogel from a solution of the sulfates of aluminum and titanium. The hydrogel is washed and dried and the resulting powder is mulled with acid and water to make an extrudable paste. The paste is extruded and the extrudates redried and calcined to finish the catalyst support. The calcined support is impregnated with a solution of the catalytic metal salts, then dried and calcined again to produce the finished catalyst. Similar to the co-precipitation methods disclosed in U.S. Pat. No. 3,401,125 the method of this patent includes washing steps which are expensive, and further, includes at least two calcining steps.
U.S. Pat. No. 3,997,431 teaches a hydrodesulfurization process using a catalyst substantially free of phosphates and consisting essentially of hydrogenating Group VIB and Group VIII metals, both hydrogenating metals being in the sulfided form, supported on a non-zeolitic refractory oxide carrier and promoted with a Group IVB metal such as titanium. The titanium may be added to the carrier simultaneously with the Group VIB and Group VIII metals and preferably after the calcination of the carrier.
U.S. Pat. No. 4,443,558 teaches a method for making a catalyst comprising alumina with Group VIB and VIII metal components wherein the method comprises peptizing alumina powder with an aqueous acidic solution of a Group VIII metal salt, neutralizing the peptized alumina/Group VIII metal with an aqueous solution of a nitrogen-containing base with a dissolved Group VIB metal salt therein, extruding, drying and calcining the catalytic particles.
While catalyst prepared according to this method show good hydroprocessing activity, there is a problem in preparing catalyst in a reproducible manner. Pore size distribution of the catalyst base vary significantly and agglomeration of the catalytic metals such as nickel and molybdenum occurs on the surface of the catalyst.
U.S. Pat. No. 4,444,655 discloses the use of a hydrotreating catalyst in a process for hydrotreating a heavy hydrocarbon oil containing asphaltenes. The hydrotreating catalyst utilizes inorganic oxides selected from Groups II, III and IV of the Periodic Table. The catalytic metal components are selected from metals belonging to Groups VB, VIB, VIII and IB of the Periodic Table.
The catalyst of the '655 patent has an average pore diameter between 180 angstroms to about 500 angstroms, with total volume of such pores being larger than about 0.2 cc/g.